Vertical design spectral response acceleration

[epajuelo]

Hi everyone. This is the first time I use IBC 2003 and I would appreciate If anyone could clarify me what is the vertical design spectral response acceleration that I have to use to dynamically analyze my strucrure. The horizontal one is clearly defined in the IBC 2003, but I can not find the vertical spectrum. Section 1617.1.1 details the combined sesimic load, but using a vertical load obtained as a proportional part of the weight. If I use that vertical load I wont consider the dynamic effects of the load. Some other codes like IBC recommends using two thirds of horziontal spectrum in vertical direction. Can anyone help me?

Thanks in adcance.

Eugenio

 

[DST148]

For one of our projects we were supplied with site-specific spectra.
The ratio of the vertical component to the horizontal motion was given as 0.72. The given spectra was scaled by 0.72 for analyzing for acceleration in the vertical direction. We used 100-40-40 method for directional combinations.
In the absence of design data, a ratio between 0.60 to 0.80 would be a good guess.